1. Field of the Invention
The invention relates to a method of regulating the throughput in the electrochemical regeneration of chromosulfuric acid by the metered addition of hot chromium (III ) sulfate solution containing sulfuric acid in continuously operated flow-type electrolysis cells.
2. Description of the Prior Art
It is known to convey the hot solution (hot chromium (III) sulfate solution), into stock containers disposed in an elevated position and to feed the electrolyte to the individual cell cascades from said stock containers by means of glass siphons and long flexible pipes. (cf. M. Kappel, Elektrolytische Regeneration von Chromsaure [Electrolytic Regeneration of Chromic Acid], Chem. Ing. Technik 35 (1963), 386-389). Said siphons are glass tubes bent in a U-shape and having an elongated limb which terminates with a capillary-type tapering of the glass tube diameter. The amount of liquid flowing through is dependent on the difference in height between the liquid level in the stock vessels and the end of the longer limb of the glass siphon, and also on the diameter of the capillary. If it is intended to alter the amount of liquid, the glass siphons have to be replaced by others having greater capillary diameter (for more passage of liquid) or smaller capillary diameter (for less passage of liquid).
This type of metered addition has a number of disadvantages:
1. The stock containers storing the hot chromium (III) sulfate solution containing sulfuric acid are an accident risk in the event of leakages. PA1 2. The chromium (III) sulfate solution containing sulfuric acid has to be fed to the electrolyte cells via long flexible pipes. Owing to entrained air and evolving gases, the flexible pipes have to be degassed in a suitable way. In addition, the gases can result in the breakdown of the liquid column in the glass siphon. PA1 3. If the amount of electric current available changes, the amount of electrolyte to be fed through has to be adapted by replacing the glass siphon. That requires some time and results in defects in the quality of the regenerated chromosulfuric acid. PA1 4. The hot chromium (III) sulfate solution containing sulfuric acid arriving from the montan wax bleaching often contains traces of wax which has not been separated off. Since the working temperature of the electrochemical regeneration (less than 100.degree. C.) is below the melting point of the wax, wax may deposit in the glass siphons and, in particular, in the capillaries of the glass siphons. This alters the diameter of the glass tubes and the amount of liquid flowing through, and consequently the quality of the final product (constant changes in concentration). PA1 1. the pipeline system is laid outside the workplaces, namely below the platform of the electrolysis cell shop; PA1 2. the electrolyte is fed into the liquid of the PA1 3. the pressurized electrolyte passes through the opening of the zirconium orifice at high velocity (turbulently). The encrustation of said opening due to solidifying wax hardly takes place any longer (in contrast to this, the capillary of the glass siphon through whose opening the liquid flowed comparatively slowly (laminarly) became encrusted). PA1 4. The slight variations in the amounts of electrolyte fed into the cascades result in slight variations in concentration in the final product if the amount of electrolysis current is constant. PA1 a) changes in the viscosity of the electrolyte corresponding to the variations in the density, PA1 b) changes in the viscosity of the electrolyte corresponding to variations in the electrolysis temperature, PA1 c) encrustations of the orifice opening of the zirconium orifice due to depositions of wax, resin and/or gypsum, PA1 d) blockages in the overflows from diaphragm pocket to diaphragm pocket within a cell, PA1 e) blockages in the overflows from cell to cell within a cascade.